I think you are mistaken about your definition of the term; "pitch".
Pixel pitch is the distance between pixels, but since sensor designers don't put dead space between pixels, it's also treated as equal to the pixel size by most of the articles I've seen. The pixel is the entire circuit, not just the light collection area. It is the microlens, Bayer filter, support circuitry and whatever else they've placed on it.
In looking for a reference, I ran into this page:
http://www.clarkvision.com/articles/does.pixel.size.matter/
It's a long article, but covers the topic I introduced about 10,000 times better. So, go there, read it and we can end the discussion here. A couple of extracts from the Conclusions section:
"Small versus large pixels matter less in modern sensors: with the low noise (read noise and camera electronics noise) available in many of today's cameras (circa 2014+) one can synthesize large pixels from a sensor with small pixels obtaining similar (or even better) performance."
"When choosing between cameras with the same sized sensor but differing pixel counts, times have changed. A decade ago, I would have chosen the camera with larger pixels (and fewer total pixels) to get better high ISO and low light performance. Today I would choose the higher megapixel (thus smaller pixels)."
So, go for a smaller pitch and, if you need the higher image quality of the larger pixels, do it in post.
My other point was that, for wildlife photographers, ignore the crop factor. Look instead at the pixel pitch ratio. A 50 MP FF and 20 MP APS-C have about the same pixel pitch. All other things being equal, the APS-C sensor doesn't provide any crop factor advantage--it just means you have fewer pixels to throw away. For a 20 MP FF and 20 MP APS-C, you do indeed have a 1.6x advantage in resolution.